Chromium plated article



Patented Dec. 8, 1931 UNITED STATES PATENT OFFICE WILLIAM J. MZERTEN, OF PITTSBURGH, PENNSYLVANIA, ASQIGNOR TO WESTINGHOUSE ELECTRIC AN D MANUFACTURING GOMPAN Y, A CORPORATION OF PENNQYLVANIA OEROMIUM PLATED ARTICLE No Drawing.

My invention relates to chromium plated articles and specifically to metal articles comprising a foundation metal and a composite coating of metals, one of which is chromium.

It is among the objects of my invention to provide means for producing an electro-plated article having an outer coating of chromium and an under coating of a metal that 10 provides a smooth foundation for the chromium and has reflective properties and color similar to that of chromium.

Another object of my invention is to provide a composite article having a chromium l6 outer coating and an under-coating of a metal, the electrolytic potential of which is intermediate chromium and copper.

My invention is useful in making chromium plated articles for general use, such as ornamental hardware, and is particularly useful in the manufacture of reflectors for lighting devices and other highly polished articles that are subjected to a rather high temperature.

Metallic chromium is useful as a reflective or protective coating in place of nickel or silver. In some respects it is preferable to nickel or silver, as it is hard and resistant to abrasion and as it has a reflectivity only 80 slightly lower than silver. Chromium is particularly resistant to heat and to the attack of corrosive agencies existing in the atmosphere. However, it is diflicult to polish chromium on account of its extreme hardness.

When an article is plated with chromium, any-of the scratches or imperfections in the foundation metal appear in the chromium plate. Consequently, the finished chromium plating is imperfect wherever a perfectly polished foundation surface is not provided. I, therefore, provide a coating of a metal over the foundation metal that is similar in color to chromium, will conceal imperfections in the foundation metal and is susceptible of being easily polished; so

-- that when the chromium is plated, a perfectly smooth reflective coating is obtained.

The metal utilized as a coating for the 50 foundation metal is cobalt. Cobalt has an Application filed. October 10, 1925. Serial No. 61,841.

electrolytical potential intermediate chromium and copper and near the electrolytic potential of iron. By referring to the electrochemical series, it will, therefore, be apparent that, when copper or nickel, or a metal intermediate copper and nickel in the electrochemical series, such as bismuth, tin or lead, is employed as the foundation metal, the intermediate layer of cobalt will have an electrolytic potential between the foundation metal and the chromium. By arranging the respective layers in this manner, the tendency for the chromium to corrode by reason of electrolytic action is decreased.

I provide an article comprising a founda-.

tion metal of iron or an alloy thereof or a non-ferrous metal such as copper or an alloy thereof, such as brass. I first produce a coating of cobalt on the foundation metal preferably by electro-plating the cobalt thereon. However, I may form a cobalt blank and build up the foundation metal on the blank by electro-plating or by other wellknown means.

The coated foundation metal is prepared for the chromium plating by carefully polishing it-in order to remove all imperfections and scratches, and then cleaning in order to remove all foreign matter.

The chromium is next deposited on the polished surface by any of the well known chromium-plating processes. The chromium may be deposited as a lustrous coating or may be deposited in the gray form and afterwards polished if a lustrous coating is desired. In all instances, the composite coating produced is homogeneous, resistant to corrosion and free from markings and scratches existing in the foundation metal.

The reflective cobalt coating also provides a surface only slightly inferior in reflectivity to chromium and which serves as a silverlike backing for the chromium in case the chromium plating is thin or becomes worn through. The composite coating, therefore, provides an article resistant to corrosion and to the effects of heat, and at the same time, provides a surface having high reflective properties and great hardness.

There is some discrepancy in the literature with respect to the designation of elements in the electro-chemical series. In the specification and claims, the table given on page 433 of the 1925 edition of Mellors glodern Inorganic Chemistry is taken as a asis. 1

Although I have described a specific embodiment of my invention, I do not wish to be limited thereto, as various changes in the details of my process and structure may be made without departing from the spirit of my invention as defined in the annexed claims.

I claim as my invention:

1. An article comprising successive layers of copper, cobalt and chromium, the chromium forming the outer layer and being electrodeposited directly on the layer of cobalt.

2. An article of manufacture comprising a foundation metal selected from a group of metals having an electrolytical potential between and including copper and nickel in the electrochemical series, a layer of cobalt thereon and a coating of chromium on said layer of cobalt.

- 3. The process of providing a smooth protective surface which comprises providing a layer of metal selected from a group of metals having an electrolytical potential between and including copper and nickel in the electrochemical series, polishing the foundation metal, electrodepositing a layer of cobalt thereon and then electrodepositing a layer of chromium on the layer of cobalt.

In testimony whereof, I have hereunto sub:

scribedmy name this 2nd day of October,

WILLIAM J. MERTEN. 

